Advice wanted: patching trunk flr/inner whl house

[Schonyenko2]

A photo assesment is always difficult, but a couple of observations are that, there's a lot of plastic in the areas around where you've ground, and I'm guessing that you'll find more in areas that you haven't disturbed yet. Also, you will need to cut past, and remove any rusted areas that you will be welding to, as you can't weld rust.
Don't forget to use weld through primer between the seems to keep rust from starting there.
My 2 cents: by the time you're done, you might have been better off replacing the inner wheelhouses, and putting in a one piece trunk floor.